The present invention relates to a disk chucking mechanism and a disk drive device, and more particularly to the art of increasing the positional accuracy of various components to provide a low-profile structure for such a disk chucking mechanism and a disk drive device.
There are known disk drive devices for recording an information signal on and reproducing an information signal from a disk-shaped recording medium such as an optical disk, or a magneto-optical disk. The known disk drive devices include a disk drive device of the type a disk chucking mechanism having a disk table for mounting a disk-shaped recording medium thereon and a chucking pulley for gripping and chucking the disk-shaped recording medium in coaction with the disk table. For details, reference should be made to Japanese Patent Laid-open No. Hei 6-180913 and Japanese Patent Laid-open No. Hei 9-265705, for example.
The disk drive device operates as follows: When a disk-shaped recording medium that is chucked by the disk table and the chucking pulley is rotated upon rotation of the disk table, an optical pickup that moves in a radial direction of the disk-shaped recording medium emits and applies a laser beam to the disk-shaped recording medium to record an information signal on or reproduce an information signal from the disk-shaped recording medium.
FIGS. 25–28 of the accompanying drawings show a conventional disk chucking mechanism a. As shown in FIGS. 25 and 26, the disk chucking mechanism a has a disk table b and a chucking pulley c.
The disk table b is fixed to a motor shaft d of a spindle motor (not shown), and has a positioning knob e projecting upwardly from the center of the disk table b. The positioning knob e may comprise the upper end of the motor shaft d which projects upwardly from the disk table b.
The spindle motor is housed in a base casing f.
The chucking pulley c has a shank g and a flange h and a presser i that are disposed respectively on upper and lower ends of the shank g. The flange h and the presser i extend outwardly from the respective upper and lower ends of the shank g.
The chucking pulley c has a downwardly open central recess defined therein and a downwardly projecting positioning tube j disposed centrally in the recess. The positioning tube j has a guide hole k defined in a lower end thereof and having a diameter progressively smaller in the upward direction, and a vertically extending insertion hole 1 joined to the upper end of the guide hole k.
The chucking pulley c has a rotary slide knob m projecting upwardly from the center of the upper surface thereof.
The chucking pulley c is rotatably supported in a support hole o that is defined in an end of a horizontally long support arm n. Specifically, the shank g of the chucking pulley c is inserted in the support hole o, and the chucking pulley c is retained on the support arm n by the flange h against dislodgment from the support arm n.
Vertical displacement pins p that are horizontally spaced from each other project laterally from the other end of the support arm n. A holder spring q is mounted on the support arm n and has a free end pressing downwardly the rotary slide knob m on the chucking pulley c.
The vertical displacement pins p slidably engage in respective cam slots s defined in a cam plate r. Each of the cam slots s has an upper horizontal section t, a slanted section u, and a lower horizontal section v which are defined successively downwardly. The cam plate r is movable horizontally.
The vertical displacement pins p also slidably engage in respective vertically long guide holes defined in a guide means (not shown).
The disk chucking mechanism a operates as follows: A disk tray x with a disk-shaped recording medium w placed thereon is moved horizontally, and then stopped when a through hole y defined in the disk tray x is positioned above the disk table b.
Then, the disk tray x is moved downwardly, or the disk table b is moved upwardly, placing the disk-shaped recording medium w on the disk table b. The disk tray x is spaced downwardly from the disk-shaped recording medium w that has been placed on the disk table b.
Then, the cam plate r is moved horizontally to cause the vertical displacement pins p to move relatively from the upper horizontal sections t through the slanted sections u into the lower horizontal sections v of the cam slots s. As the vertical displacement pins p also slidably engage in the respective vertically long guide holes, the support arm n is moved downwardly, and so is the chucking pulley c. The presser i of the chucking pulley c is pressed against the disk-shaped recording medium w by the holder spring q. The disk-shaped recording medium w is now gripped and chucked on the disk table b by the disk table b and the chucking pulley c.
When the chucking pulley c is moved downwardly, the positioning knob e of the disk table b slides into the guide hole k in the positioning tube j and is inserted into the insertion hole l. The disk table b and the chucking pulley c are now centrally aligned with each other vertically, so that the chucking pulley c is positioned with respect to the disk table b.
The disk-shaped recording medium w thus chucked in place is then rotated in unison with the chucking pulley c by the disk table b that is rotated by the spindle motor. The chucking pulley c is rotated while the rotary slide knob m is being held by the holder spring q and the shank g, the flange h, and the presser i are being spaced from the support arm n. The disk table b and the disk-shaped recording medium w are rotated out of contact with other components.
Since the disk table b, the chucking pulley c, and the disk-shaped recording medium w are rotated out of contact with other components, the disk-shaped recording medium w is prevented from vibrating due to contact with other components. Since the disk-shaped recording medium w is not vibrated, the optical pickup is capable of operating stably in its focus servo and tracking servo processes for thereby preventing errors from occurring when recording an information signal on and reading an information signal from the disk-shaped recording medium w.
However, the conventional disk chucking mechanism a is problematic in that the support arm n has a poor positional accuracy because the holder spring q presses the chucking pulley c against the disk-shaped recording medium w.
The positional accuracy of the support arm n will be described below with reference to FIG. 25 of the accompanying drawings. FIG. 25 shows the support arm n as being exaggeratedly inclined in order to explain the positional accuracy of the support arm n.
The vertical displacement pins p and the cam slots s in the cam plate r suffer positional accuracy variations. It is assumed that the sum of vertical accuracies of the vertical displacement pin p that is positioned remoter from the chucking pulley c and the cam slot s receiving that vertical displacement pin p is represented by P1, the sum of vertical accuracies of the vertical displacement pin p that is positioned closer to the chucking pulley c and the cam slot s receiving that vertical displacement pin p by P2, the distance between the vertical displacement pins p by L1, and the distance between the vertical displacement pin p that is positioned remoter from the chucking pulley c and the center of the chucking pulley c by L2.
Since the support arm n is positionally displaced vertically due to changes in the biasing force of the holder spring q that is used in the disk chucking mechanism a, the chucking pulley c cannot provide a reference for the vertical positional accuracy of the support arm n. As the sum H1 of the accuracies of the vertical displacement pins p is expressed as H1=P1+P2, the vertical accuracy H2 of the support arm n at the central position of the chucking pulley c is given by the following equation:H2=H1×L2/L1=(P1+P2)×L2/L1  (1)
Usually, the vertical displacement pins p are positioned radially outwardly of the outer circumferential edge of the disk-shaped recording medium w for the purpose of making the disk chucking mechanism a lower in profile, and the distance L1 between the vertical displacement pins p is minimized in order to reduce the size of the outer contour of the disk chucking mechanism a. Accordingly, the distance L2 tends to be several times greater than the distance L1, and the sum H2 also tends to be several times greater than the sum H1, with the result that the positional accuracy of the support arm n at its distal end is very poor.
Inasmuch as the positional accuracy of the support arm n at its distal end, i.e., the positional accuracy of the support arm n at its portion supporting the chucking pulley c, it is necessary to increase the axial length of the shank g in order to prevent the chucking pulley c from contacting other components when the chucking pulley c is in rotation. However, an increase in the axial length of the shank g presents an obstacle to efforts to construct the disk chucking mechanism a in a low-profile configuration.
The angular accuracy of the support arm n will be described below.
As shown in FIG. 25, if the support arm n is inclined an angle θc to the horizontal plane, then the angle θc is expressed as Tan θc=H1/L1. If the chucking pulley c has a diameter Dp, then a displacement Δh of the chucking pulley c at its central position is given by the following equation:
                                                                        Δ                ⁢                                                                  ⁢                h                            =                            ⁢                                                                                          Dp                      /                      2                                        ·                    Tan                                    ⁢                                                                          ⁢                  θ                  ⁢                                                                          ⁢                  c                                =                                  H1                  ×                                      Dp                    /                    2                                    ⁢                  L1                                                                                                        =                            ⁢                                                (                                      P1                    +                    P2                                    )                                ×                                  Dp                  /                  2                                ⁢                L1                                                                        (        2        )            
When the disk-shaped recording medium w is chucked in place on the disk table b, if the support arm n is inclined to the horizontal plane, then the support arm n and a portion of the chucking pulley c are liable to contact each other. In an attempt to avoid such contact, it is necessary to elongate the shank g axially in view of the displacement Δh. While the disk-shaped recording medium w is not being chucked in place, the chucking pulley c can move freely with respect to the support arm n by a distance which is made greater as the shank g is axially elongated. The increased axial length of the shank g, however, prevents the disk chucking mechanism a from being lower in profile.
As shown in FIG. 26 of the accompanying drawings, the flange h of the chucking pulley c needs to be spaced from the support arm n by a certain distance C1, and the presser i of the chucking pulley c needs to be spaced from the support arm n by a certain distance C2 in order to avoid contact between the chucking pulley c and the support arm n when the chucking pulley c is in rotation. If the distances C1, C2 are to be maintained and at the same time the disk chucking mechanism a is to be of a low profile, then it is desirable to reduce the thickness of the support arm n.
However, there is a certain limitation on efforts to reduce the thickness of the support arm n because the support arm n has to have a certain level of rigidity to achieve desired mechanical strength. As a result, the axial length of the shank g has to be increased to maintain the distances C1, C2. Accordingly, the thickness of the chucking pulley c is also increased, and the chucking pulley c moves vertically an increased distance, making it difficult to make the disk chucking mechanism a lower in profile.
The relationship between the size of the support hole o in the support arm n and the thickness of the disk chucking mechanism a will be described below with reference to FIG. 26.
The disk table b and the chucking pulley c need to be centrally aligned with each other in order to reduce vibrations caused when they are in rotation. The centers of the disk table b and the chucking pulley c are brought into accurate alignment with each other by inserting the positioning knob e of the disk table b into the positioning tube j of the chucking pulley c.
At this time, since the chucking pulley c is freely movable in the support hole o in the support arm n, the positioning tube j has the guide hole k, and the positioning knob e is guided by the guide hole k to move reliably into the insertion hole 1 when the chucking pulley c is moved downwardly.
If the positioning knob e is located within the diameter (introducing range) Dθ of the lower end of the guide hole k, then the positioning knob e can be inserted into the insertion hole 1. If the vertical length Hc of the guide hole k is constant, then the introducing range Dθ can be increased by reducing the introducing angle θ of the guide hole k. However, if the introducing angle θ is reduced, then the ability of the positioning knob e to slide into the guide hole k is also reduced. Therefore, the introducing angle θ is limited to a certain range.
For reliably inserting the positioning knob e into the insertion hole 1, it is necessary to keep the introducing angle θ constant and increase the introducing range Dθ. If the introducing range Dθ is increased, then the vertical length Hc of the guide hole k is increased accordingly, resulting in an increase in the thickness of the disk chucking mechanism a.
The introducing range Dθ depends upon the magnitude of the outside diameter of the shank g of the chucking pulley c with respect to the support hole o in the support arm n. For example, if the outside diameter of the shank g is small with respect to the support hole o, then since the shank g can move freely in the support hole o within a large range, the introducing range Dθ is large. Conversely, if the outside diameter of the shank g is large with respect to the support hole o, then since the shank g can move freely in the support hole o within a small range, the introducing range Dθ is small.
To avoid contact between the support arm n and the chucking pulley c while the chucking pulley c is in rotation, the diameter of the shank g needs to be of a certain value or less with respect to the support hole o. Therefore, the introducing range Dθ needs to be of a certain value or more, and the vertical length Hc of the guide hole k is large.
The introducing range Dθ also depends upon the positional accuracy of the support arm n. For example, when the support arm n is moved vertically, if the support arm n is displaced radially of the support hole o, then the center of the chucking pulley c is displaced accordingly out of alignment with the center of the disk table b. Therefore, it is necessary to increase the introducing range Dθ.
As the introducing range Dθ becomes larger, the vertical length Hc of the guide hole k increases, and the thickness of the disk chucking mechanism a increases.